1. Field of the Invention
This specification relates to a method for controlling a drying machine (dryer) capable of drying clothes and the like, and more particularly, a method for controlling a drying machine capable of improving energy efficiency and reducing a drying time in a more efficient stable manner by selectively using at least one of a heat pump system and a heater as a heat source to heat up air, which is used for drying a target to be dried.
2. Background of the Invention
In general, a clothes treating apparatus having a drying function such as a washing machine or a drying machine (dryer) dries laundry (clothes) by putting the laundry, which are completely washed and dehydrated (spin-dried), into a drum, supplying hot air into the drum, and evaporating moisture of the laundry.
For example, a laundry drying machine includes a drum rotatably installed in a main body and receiving laundry therein, a driving motor to drive the drum, a blowing fan to blow air into the drum, and a heating unit to heat air introduced into the drum. The heating unit may use thermal energy generated using electric resistance or heat of combustion generated by burning gas.
In the meantime, the air discharged out of the drum of the drying machine contains moisture of the laundry filled in the drum so as to become hot and humid. Here, the drying machines are classified, according to how to process the hot humid air, into a circulating type drying machine, in which hot humid air circulates without being discharged out of the drying machine and is cooled below a dew point temperature through a heat exchanger such that moisture contained within the hot humid air can be condensed for resupply, and an exhaust type drying machine, in which hot humid air passed through the drum is discharged directly to the outside of the drying machine.
For the circulating type drying machine, in order to condense the air discharged out of the drum, the air has to be cooled below the dew point and then heated up by the heating unit prior to being resupplied into the drum. When a heater is used as the heating unit, a heat exchanger is separately needed to condense the hot humid air discharged from the drum, and thermal energy supplied by the heater is discharged to the outside due to heat exchange with the heat exchanger. The circulating type drying machine has an advantage of sufficiently supplying thermal energy needed by using the heater, but cause problems of lowering thermal efficiency and raising energy consumption. Also, for air circulation, since moisture has to be fully removed, the size of the heat exchanger or a drying time may increase.
Even for the exhaust type drying machine, after hot humid air is discharged to the outside, external air of room temperature has to be introduced and heated up to a required temperature through the heating unit. When a heater is used as the heating unit in the exhaust type drying machine, it has advantages in that any heat exchanger is not required separately and a drying time is reduced owing to fully supplying necessary thermal energy using the heater. However, air of high temperature is discharged directly to the outside with containing thermal energy transferred by the heating unit. This may result in lowered thermal efficiency and high energy consumption.
Therefore, in recent time, a drying machine capable of enhancing energy efficiency in a manner of restoring unused energy from air discharged out of a drum and using the restored air for heating air to be supplied into the drum has been introduced. One example of such drying machine is a drying machine having a heat pump system. The heat pump system includes two heat exchangers, a compressor and an expansion apparatus. Accordingly, a refrigerant circulating in a system adsorbs energy contained in hot air discharged and the adsorbed energy is used for heating air to be supplied into the drum. This may result in an increase in energy efficiency.
In detail, the heat pump system includes an evaporator disposed at an outlet side of the drum, and a condenser disposed at an inlet side of the drum. Accordingly, a refrigerant adsorbs thermal energy through the evaporator and is heated up to a state of high temperature and high pressure by the compressor. Afterwards, the thermal energy of the refrigerant is transferred to air introduced into the drum through the condenser. This may allow for generation of hot air by using dissipated energy with unused.
However, for the drying machine with the heat pump system, the system performance may depend on capacities of the evaporator for adsorbing thermal energy, the condenser for discharging energy and the compressor for compressing the refrigerant. Therefore, the heat pump system may be ideally designed to be suitable for thermal energy necessary, but in reality, the volumes and capacities of the compressor employed in the drying machine and the condenser and the evaporator as the heat exchangers may be merely limited. Therefore, when the heat pump system is used as a heating unit for heating air to be supplied into the drum, such drying machine has the advantage of superior energy efficiency, but has a problem in that the drying time increases due to the limit of the capacity of the heat pump system. Also, in view of the characteristic of the heat pump system, an overload may occur in the compressor and the like, and this may lower reliability of the heat pump system.